Same attack using XSS as vector.
Imagine that https://xss-doc.appspot.com is a site about gift cards.
The XSS payload below will create a giftcard.htm file in the default
download folder.
If the victim open the file a GET to
https://mail.google.com/mail/u/0/#inbox will be submitted.
After the GET the file will perform a POST to
http://192.168.1.36/req.php using the GET response as a body.
An attacker would be able to read all the emails in the following requests.
I tested on Win7SP1 and IE11 with all patches and it worked.